Many plasma treatments have been described for various polymers, whereby a number of quite different plasmas have been suggested. Frequently, plasmas of noble gases are specified, but oxygen and nitrogen plasmas also are used. The aim of plasma treatment is usually to modify the surface of the polymers with the objective of improving adhesion of coating or finishing agents. A further, often described treatment objective is an improvement in dye affinity.
The literature also cites treatable polymers that can be employed for antiballistically effective materials, such as aromatic polyamide fibers or polyethylene fibers spun using the gel spinning process. In the plasma treatment of these fibers as well, changes in properties, as noted above, are always the focus of attention.
Combined treatments are sometimes suggested, comprising pretreatment in a plasma followed by wet treatment by dip impregnation with various finishing agents.
For example, JP-A 63-223 043 describes a treatment of aromatic polyamide fibers in an argon, oxygen, or nitrogen plasma. This is followed by a treatment with a gaseous or liquid mixture of dienes and compounds containing glycidyl groups. The aim is to improve the dyeing characteristics of the fibers and the adhesion of finishing agents to the fiber surface.
Additional two-stage processes with a plasma pretreatment of aromatic polyamide fibers and a subsequent wet treatment by dip impregnation, such as with polymerizable substances, are described in EP-A 191 680, EP-A 192 510, and CA-A 1 122 566. In all these processes, an improvement in the adhesion of coating or finishing agents is sought by modifying the surface via plasma treatment.
Although these processes allow good adhesion between the base material, made from aromatic polyamide fibers, and the finishing or coating agent, they are very cost-ineffective due to the requirement for treatment in two very different apparatuses (plasma treatment for the first stage and dip or coating apparatus for the second stage). Furthermore, the wet treatments of the second stage are questionable on ecological grounds.
A plasma treatment for a series of very different fiber materials is described in EP-A 492 649. This case involves treatment in a plasma of polymerizable gases, including alkenes and fluorinated alkenes. These gases are possibly "diluted" with noble gases. The objective of the treatment is an improvement of the dyeing characteristics and a positive influence on the working properties of sewing threads.
A combined plasma treatment of polyethylene with noble gases and fluorocarbons is described in U.S. Pat. No. 3,740,325. In this case, the objective is to improve the corrosion resistance by means of plasma treatment.
None of these processes indicates how plasma treatment of antiballistically effective materials must be conducted.
The improvement of the antiballistic effect is a continuing objective of manufacturers of clothing protecting against bullets and splinters as well as of suppliers of the materials employed. It must be noted that an improvement of the antiballistic effect is sought not only in the dry state but that this effect, especially with respect to the requirements of protective clothing for military applications, must be continually improved in the wet state as well.
To satisfy the demands for good antiballistic efficacy in the wet state, flat-shaped structures made from aromatic polyamide fibers have frequently been subjected to bath treatment with hydrophobically acting agents, particularly fluorocarbon compounds. Aside from the expense required for the bath treatment and subsequent drying, a wet treatment with such compounds is also questionable ecologically.
The object is therefore to develop a cost-effective process that improves the antiballistic effectiveness in the dry and, particularly, the wet state while offering the opportunity to dispense with the heretofore employed wet treatment.